Colorado is home to five species of pocket mice; the Great Basin pocket mouse, the hispid pocket mouse, the plains pocket mouse, the silky pocket mouse, and the olive-backed pocket mouse. Pocket mice are smaller cousins of kangaroo rats. Most movement is quadrupedal (using four legs), and they hunker down on their hind legs while feeding, packing their cheek-pouches with their dainty forepaws. The smallest species is the silky pocket mouse, about four inches long and weighing just one-fifth of an ounce; the largest is the hispid pocket mouse, twice that long and ten times as heavy. All but the hispid pocket mouse (which is large and has distinctly harsh, bristly fur) are difficult to distinguish from each other.
Range: The Great Basin pocket mouse occurs only in the northwest, and the hispid pocket mouse lives on the eastern plains. The plains and silky pocket mice live on the plains as well, but also in the San Luis Valley and on the Colorado Plateau. The olive-backed pocket mouse lives in the northwest and also at the foot of the Front Range.
Habitat: The nocturnal animals make extensive burrows that are plugged during the day.
Diet: Pocket mice eat mostly seeds of grasses and forbs. Seeds stored for winter but unused for food may germinate and help reestablish grassy prairies. When grain is taken, it mostly is gleaned from the ground; the mice are too small to harvest wheat themselves.
Reproduction: Active year-round, pocket mice seem to breed throughout the warmer months, producing litters of two to nine young after gestation periods of around four weeks. Owls are major predators, and owl pellets are a major source of information on the distribution of these secretive animals.
By David M. Armstrong
Department of Ecology & Evolutionary Biology
Environmental Studies Program, University Museum of Natural History
University of Colorado-Bouldermausmann@aol.com